Characterization of picosecond pulse amplification in an erbium-doped fiber amplifier using frequency-resolved optical gating

A clear understanding of the effect of resonant dispersion on picosecond pulse amplification in erbium-doped fiber amplifiers (EDFA), is important for high-capacity soliton systems. To characterize the EDFA pulse amplification the usual technique involves the separate measurement of the pulse characteristics at the input and output of the amplifier in the time and frequency domain. For pulse durations <10 ps this is normally carried out with measurements of the optical intensity autocorrelation function and the optical power spectrum. However these techniques do not provide complete characterization of the optical pulses. A new measurement technique, called frequency-resolved optical gating (FROG) has recently been developed, which can overcome the limitations of the existing techniques, and which allows the complete characterization of the intensity and phase of an arbitrary ultrashort pulse. A typical experimental setup for FROG measurements based on second-harmonic generation (SHG) in a nonlinear crystal (which is the technique we have used) is shown. The FROG trace produces a two-dimensional signal depending on time and frequency. From this signal the original electric field of the pulse can be obtained using an iterative algorithm. In our experiments we have used the SHG FROG technique, along with the standard measurement techniques (autocorrelation and spectrum), to examine EDFA pulse amplification at different wavelengths